fix: report existing PR instead of failing on follow-ups

apps/agent/agent/middleware/open_pr.py

@@ -98,12 +98,15 @@ async def open_pr_if_needed(
 
         if "success" in pr_payload:
             pr_url = pr_payload.get("pr_url")
+            pr_existing = bool(pr_payload.get("pr_existing", False))
             error = pr_payload.get("error")
             if linear_issue_id and last_message_content:
                 if pr_url:
-                    comment = f"""**Pull Request Created**
+                    header = "Pull Request Updated" if pr_existing else "Pull Request Created"
+                    action = "updated the existing" if pr_existing else "created a"
+                    comment = f"""**{header}**
 
-I've created a pull request to address this issue:
+I've {action} pull request to address this issue:
 
 {pr_url}
 
@@ -212,7 +215,7 @@ I've created a pull request to address this issue:
             base_branch = await get_github_default_branch(repo_owner, repo_name, github_token)
             logger.info("Using base branch: %s", base_branch)
 
-            pr_url, pr_number = await create_github_pr(
+            pr_url, pr_number, pr_existing = await create_github_pr(
                 repo_owner=repo_owner,
                 repo_name=repo_name,
                 github_token=github_token,
@@ -227,9 +230,11 @@ I've created a pull request to address this issue:
 
         if linear_issue_id and last_message_content:
             if pr_url:
-                comment = f"""**Pull Request Created**
+                header = "Pull Request Updated" if pr_existing else "Pull Request Created"
+                action = "updated the existing" if pr_existing else "created a"
+                comment = f"""**{header}**
 
-I've created a pull request to address this issue:
+I've {action} pull request to address this issue:
 
 **[PR #{pr_number}: {pr_title}]({pr_url})**
 

apps/agent/agent/tools/commit_and_open_pr.py

@@ -109,6 +109,7 @@ def commit_and_open_pr(
         - success: Whether the operation completed successfully
         - error: Error string if something failed, otherwise None
         - pr_url: URL of the created PR if successful, otherwise None
+        - pr_existing: Whether a PR already existed for this branch
     """
     try:
         config = get_config()
@@ -190,7 +191,7 @@ def commit_and_open_pr(
         base_branch = asyncio.run(
             get_github_default_branch(repo_owner, repo_name, github_token)
         )
-        pr_url, _pr_number = asyncio.run(
+        pr_url, _pr_number, pr_existing = asyncio.run(
             create_github_pr(
                 repo_owner=repo_owner,
                 repo_name=repo_name,
@@ -207,9 +208,15 @@ def commit_and_open_pr(
                 "success": False,
                 "error": "Failed to create GitHub PR",
                 "pr_url": None,
+                "pr_existing": False,
             }
 
-        return {"success": True, "error": None, "pr_url": pr_url}
+        return {
+            "success": True,
+            "error": None,
+            "pr_url": pr_url,
+            "pr_existing": pr_existing,
+        }
     except Exception as e:
         logger.exception("commit_and_open_pr failed")
         return {"success": False, "error": f"{type(e).__name__}: {e}", "pr_url": None}

apps/agent/agent/utils/github.py

@@ -114,7 +114,7 @@ async def create_github_pr(
     head_branch: str,
     base_branch: str,
     body: str,
-) -> tuple[str | None, int | None]:
+) -> tuple[str | None, int | None, bool]:
     """Create a GitHub pull request via the API.
 
     Args:
@@ -127,7 +127,7 @@ async def create_github_pr(
         body: PR description
 
     Returns:
-        Tuple of (pr_url, pr_number) if successful, (None, None) otherwise
+        Tuple of (pr_url, pr_number, pr_existing) if successful, (None, None, False) otherwise
     """
     pr_payload = {
         "title": title,
@@ -144,8 +144,8 @@ async def create_github_pr(
         repo_name,
     )
 
-    try:
-        async with httpx.AsyncClient() as http_client:
+    async with httpx.AsyncClient() as http_client:
+        try:
             pr_response = await http_client.post(
                 f"https://api.github.com/repos/{repo_owner}/{repo_name}/pulls",
                 headers={
@@ -162,10 +162,20 @@ async def create_github_pr(
                 pr_url = pr_data.get("html_url")
                 pr_number = pr_data.get("number")
                 logger.info("PR created successfully: %s", pr_url)
-                return pr_url, pr_number
+                return pr_url, pr_number, False
 
             if pr_response.status_code == HTTP_UNPROCESSABLE_ENTITY:
                 logger.error("GitHub API validation error (422): %s", pr_data.get("message"))
+                existing = await _find_existing_pr(
+                    http_client=http_client,
+                    repo_owner=repo_owner,
+                    repo_name=repo_name,
+                    github_token=github_token,
+                    head_branch=head_branch,
+                )
+                if existing:
+                    logger.info("Using existing PR for head branch: %s", existing[0])
+                    return existing[0], existing[1], True
             else:
                 logger.error(
                     "GitHub API error (%s): %s",
@@ -176,11 +186,41 @@ async def create_github_pr(
             if "errors" in pr_data:
                 logger.error("GitHub API errors detail: %s", pr_data.get("errors"))
 
-            return None, None
+            return None, None, False
 
-    except httpx.HTTPError:
-        logger.exception("Failed to create PR via GitHub API")
-        return None, None
+        except httpx.HTTPError:
+            logger.exception("Failed to create PR via GitHub API")
+            return None, None, False
+
+
+async def _find_existing_pr(
+    http_client: httpx.AsyncClient,
+    repo_owner: str,
+    repo_name: str,
+    github_token: str,
+    head_branch: str,
+) -> tuple[str | None, int | None]:
+    """Find an existing PR for the given head branch."""
+    headers = {
+        "Authorization": f"Bearer {github_token}",
+        "Accept": "application/vnd.github+json",
+        "X-GitHub-Api-Version": "2022-11-28",
+    }
+    head_ref = f"{repo_owner}:{head_branch}"
+    for state in ("open", "all"):
+        response = await http_client.get(
+            f"https://api.github.com/repos/{repo_owner}/{repo_name}/pulls",
+            headers=headers,
+            params={"head": head_ref, "state": state, "per_page": 1},
+        )
+        if response.status_code != 200:  # noqa: PLR2004
+            continue
+        data = response.json()
+        if not data:
+            continue
+        pr = data[0]
+        return pr.get("html_url"), pr.get("number")
+    return None, None
 
 
 async def get_github_default_branch(

apps/agent/agent/webapp.py

@@ -575,6 +575,9 @@ async def process_linear_issue(  # noqa: PLR0912, PLR0915
     bot_message_prefixes = (
         "🔐 **GitHub Authentication Required**",
         "✅ **Pull Request Created**",
+        "✅ **Pull Request Updated**",
+        "**Pull Request Created**",
+        "**Pull Request Updated**",
         "🤖 **Agent Response**",
         "❌ **Agent Error**",
     )
@@ -759,6 +762,9 @@ async def linear_webhook(  # noqa: PLR0911, PLR0912, PLR0915
     bot_message_prefixes = [
         "🔐 **GitHub Authentication Required**",
         "✅ **Pull Request Created**",
+        "✅ **Pull Request Updated**",
+        "**Pull Request Created**",
+        "**Pull Request Updated**",
         "🤖 **Agent Response**",
         "❌ **Agent Error**",
     ]